Diminished alveolar complexity and vascular development of the lung is a constant feature of bronchopulmonary dysplasia (BPD). It persists even now that oxygen therapy is used at much lower levels than 1-2 decades ago. The lung develops at low, fetal oxygen concentrations (3-5%), and, in vitro, it develops much better at these levels than in 21%. Endothelial and vascular growth is impaired at these higher oxygen levels. Epithelial and alveolar development, in turn, depend on critical interactions with the developing vasculature. Thus, the distal airways of fetal lung in 21% show much less branching. Angiogenesis is proceeding rapidly in the third trimester of gestation. Hypoxia-inducible factors HIF- 1 and -2 (HIFs) regulate critical growth factors, receptors, kinases, and other proteins in angiogenesis. Oxygen tension is the primary regulator of HIF- 1alpha and -2alpha, the key components of these transcription factors. Knocking down HIF-2 in lung throughout gestation, or in distal lung epithelium during the third trimester, results in oversimplified lung development and respiratory distress in newborn mice. Recently HIF prolyl-4- hydroxylases (P4Hs or PHDs) were found to catalyze O2-dependent degradation of HIFs. Inhibiting P4Hs with oxoglutarate analogs or iron chelators stabilize HIFs, increase VEGF, and cause angiogenesis. HIFspecific P4H inhibitors are being rapidly developed. In trials in cardiovascular medicine, angiogenic therapy with single growth factors has caused formation of dysmorphic or leaky vessels. "Flipping the switch" of HIFs in the normoxic lung can cause more balanced angiogenesis. We hypothesize that loss of HIFs promotes lung hypoplasia in BPD, and that stabilizing HIFs will promote more normal lung development in the premature neonate with evolving BPD. This proposal is for translational research to test the effect of new HIF-specific P4H inhibitors on lung in vitro and in vivo using the primate model of BPD. In vitro, P4H inhibition causes HIF-1alpha stability, VEGF expression, angiogenesis, and increased activity of kinases important in vascular growth. In lung explants, new HIF P4H inhibitors will be tested for their ability to stabilize HIFs and increase HIF-related proteins and kinase activities. In addition, HIF P4H inhibitor will be administered intravenously, intratracheally, and by both routes combined. Gas exchange, pulmonary mechanics and function, various clinical parameters, and HIF P4H inhibitor levels will be measured in vivo, and alveolar and vascular development, lung HIF proteins and HIF-related proteins and kinase activities, and tissue HIF P4H inhibitor levels will be quantitated ex vivo. Therapy at the level of HIF transcription factors to improve angiogenesis and alveolar development offers promise to prevent BPD.